Because many (if not most) people mistakenly think that herpes is exclusively a sexually transmitted disease. (It's actually a virus family, like the common cold; many members of which are transmissible via social or familial contact.) The reporter probably didn't want the headline to risk stigmatizing the elderly or "forgetful" by those too quick to judge.

Well, they do in the actual article. But I agree -- there is little need to hide the name of a virus, especially when most of humanity has a form of it.

Such "hiding" is only effective against those ignorant about such viruses. This is likely the same sub-population who would react negatively.

How would you write it out? HSV-1 is the virus typically responsible for cold sores. The other herpes viruses were not under investigation, and writing out "herpes simplex virus 1" is longer and more confusing to the layman than "cold sore virus".